One of the best ways I have found to enter into a discussion of Sif Figs or more importantly uncertanty in measuerment is to wait until you cover density or the first lab you make measurements and calculations. Some students will round their answers ot 1 or 2 figures others will give you calculator answers with 6-7. When you return the labs raise the question of who is right. Actually do a high and low calculation. In otherwords take each measurement at its maximum and minimum estimated values and calculate how high andlow the ansersr could be. (balances have tolerances printed on them). You can easily show the students that only the numbers included in both the high and low are reliable. I then explain that rather than calculate a high and low value we use Sig figs to provide a rough estimmat of degree of precision that our answers should reflect. Since Sig figs do not appear on any of the state standards I usualy tell my students to round answers to three Sif Figs which is about the limit of what we can actually measure n our Labs.

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